Printing apparatus employing stepping motor control system

ABSTRACT

A stepping motor control system for controlling the bidirectional movement of a plurality of styli across a recording medium. The control system includes a feedback path for energizing selected styli at predetermined intervals whereby substantially distortion free characters are printed on the recording medium. The styli, in a preferred embodiment, are etched on a strip of insulating material and driven by the stepping motor within a slotted support member.

[451 May 7,1974

Unite States Patent 1 Casperson et a1.

[ PRINTING APPARATUS EMPLOYING Cone................ 346/74 M 8/1972Stange 346/139 A 1/1965 Schiebeler....,.................... 346/74 E3,363,261 1/1968 Maiershofer 3,576,584 4/1971 STEPPING MOTOR CONTROLSYSTEM Inventors: John H. Casperson; George N.

Tsilibes, both of Rochester, NY.

Assignee: Xerox Corporation, Stamford,

Primary Examiner-Stan1ey M. Urynowicz, Jr. Assistant ExaminerJay P.Lucas Conn.

[22] Filed: July 3, 1972 ABSTRACT A stepping motor control system forcontrollin bi-directional movement of a pluralit recording medium. Thecontrol 21 Appl. No.: 268,354

feedback path for energizing select mined intervals whereby substantial]characters are printed on the record styli, in a preferred embodiment ofinsulating material and driven b motor within a slotted support membe3,427,633 2/1969 Waterman 346/74 S 9 Claims, 5 Drawing Figures CHARACTERGENERATOR SHAFT ENCODER STEPPING MOTOR CONTROL CIRCUIT TENTEnaAY 71914 Iv 3810.189

sum 1 0r 4 STEPPING MOTOR CONTROL CIRCUIT ENCODER CHARACTER GENERATORPAl'EM'EHMAY 1 19m 3610.189

saw u or 4 mm wwm Q VAT A w NM .wwm QNM $9M} O KOPOE ozrmmmkw M QRPRINTING APPARATUS EMPLOYING STEPIING MOTOR CONTROL SYSTEM BACKGROUND OFTHE INVENTION The quality of recording at a low noise levelcharacteristic of non-impact printers has contributed to makeelectrographic printing, or recording, attractive in various commercialapplications. As is well known, electrography, as it relates to thepresent invention, may be defined as the deposition of electrostaticcharge on an insulating recording medium in a charge patterncorresponding to the information to be recorded. The charge pattern isdeveloped to provide a visible representation of the recordedinformation.

The conventional technique of matrix printing has particular usefulnessin electrographic recording. In this technique, a linear array of astyli are driven across the recording medium at a constant speed and, asvarious signal voltages are applied to the styli, alphanumeric chargepatterns are recorded as portions of a two-dimensional matrix. Forexample, ifa five by seven character matrix is utilized, by selectivelypulsing the styli corresponding to the desired character, a latentelectrostatic image corresponding to the selected character will beformed within the confines of the five by seven matrix. Development ofthe latex electrostatic charge converts the otherwise latent patterninto a visible recording. This may be done by applying to the latentcharge pattern electroscopic marking particles, commonly referred to astoner, and charged to a polarity opposite to that of the latent chargepattern. Cascade or brush development, among others, may be used forapplying the toner. Fusing the toner to the recording medium,which-renders the visible recording permanent on the recording medium,may be accomplished with heat, flash fusing, organic solvents, pressure,etc.

Prior art printers of a matrix type generally use varied mechanicaltechniques for driving the styli across the recording medium to print aline at a time. In particular, the prior art matrix printers generallyincluded clutches, gear trains, solenoids and various other mechanicalelements to drive the styli. The speed and accuracy of the printers arelimited by the mechanical elements utilized. Further, the number ofmechanical elements in the prior art drive systems lead to high wear ofthe elements. Therefore, the prior art electrographic drive systems havebeen generally unattractive due to the cost, limited speeds, high wearrates, and the unreliability ofa drive system utilizing a large numberof mechanical and electromechanical components.

SUMMARY OF THE PRESENT INVENTION The present invention relates generallyto an electrographic recording technique wherein a plurality of styliare driven across, and in contact with, a recording medium by a steppingmotor, the stepping motor being driven and controlled by a novel controlsystem in accordance with the principles of this invention. Inparticular, a plurality of electrical conductors or styli, correspondingto the number of rows of the character ma trix, are connected to acarrier member. The carrier member is inserted into a carrier guidewhich includes a slotted portion to allow a driving member access to thecarrier member. The driving member, comprising an engagement meansmounted onto the shaft of the stepping motor, is placed adjacent thecarrier guide whereby the engagement means engages the carrier member.When the stepping motor is energized, the carrier member is incrementedfrom an initial position within the carrier guide in a manner totraverse the recording medium so that the styli may be controlled toprint a complete line of characters. After a line is printed, thestepping motor is driven in the reverse direction to return the styli tothe initial position. The stepping motor may be driven continuously orin a compose, or low speed mode, or a print, or high speed mode,dependent upon the input to the printer.

It is an object of the present invention to provide a novel stylus drivecontrol system for use in an electrographic printer.

It is a further object of the present invention to provide a novelstylus drive control system for controlling an electrographic stylus,the stylus being driven by a stepping motor. In the preferred mode ofoperation, the stylus comprises a plurality of conductors forming on astylus carrier member, the stylus carrier being driven between first andsecond positions within a carrier guide by the stepping motor.

It is still a further object of the present invention to provide avnovel stylus drive system which utilizes a stepping motor and a novelstepping motor control circuit which provides a reliable, economical andaccurate method of driving an electrographic stylus across a recordingmedium.

It is a further object of the present invention to provide a novelstylus carrier which has a low mass, can be driven at high rates ofspeed, is economical, has a high index of durability and a low wearrate.

DESCRIPTION OF THE DRAWING For a better understanding of the inventionas well as other objects and further features thereof, reference is madeto the following description which is to be read in conjunction with theaccompanying drawing wherein:

FIG. 1 is a perspective view of an electrographic recording apparatusutilizing the novel stylus drive system of the present invention;

FIG. 2 is a plan view of the stylus carrier of the present invention;

FIG. 3 illustrates in block diagram form the novel circuitry forcontrolling the apparatus of FIG. I in accordance with the teachings ofthe present invention;

FIG. 4 is a schematic diagram of the stepping motor control logic; and

FIG. 5 is a schematic diagram of the stepping motor drive circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, aninsulating recording medium 2, such as plastic coated paper, is shownsupported in a recording zone generally by a backing electrode 4 whichholds the recording medium 2 against pressure contact by a plurality ofstyli 6.

This plurality of styli may be formed in a linear array and may includea series of parallel conductive electrodes suitably electricallyisolated from one another as shown in FIG. 2. The array is etched on aninsulating medium, or carrier member 8, such as Mylar, through whichelectrical recording signals are supplied individually to selected stylicorresponding to the character to The technique for producingalphanumeric characters by selectively pulsing corresponding styliwithin a matrix of styli is well known. In the preferred embodiment,character generator 1 causes motion to be imparted to the stylus carriermember 8 by stepping motor 10, the shaft 12 of which is coupled to anengaging member 14. A shaft encoder 16 is also mounted on shaft 12.Stepping motor control circuit 18 is coupled to stepping motor andresponds to signals from character generator 1 to control theincrementing of motor 10. Any motor which is capable of high speedincrementing may be used as stepping motor 10, such as Model Ts25,manufactured by the Superior Electric Company, Bristol, Conn.

Engaging member 14 is mounted adjacent to slot portion 20 of styluscarrier guide 22. Stylus carrier guide 22 is illustratively U-shaped andincludes a channelshaped opening 24. The stylus carrier member,generally indicated by reference numeral 30, is flexible and includes aplurality of styli, or conductors, 6 corresponding to the number of rowsin the character matrix, as shown in FIG. 2 Carrier member is insertedwithin the slottedcarrier guide 22. Also included on stylus carriermember 30 are a plurality of perforations 3 4. Stylus carrier member 30illustratively comprises a belt made ofa double layer of Mylar and has aplurality of stainless steel conductors etched thereon. At theright-hand end of member 30 is connector 36 for connecting styli 6 tocharacter generator 1. As flexible carrier member 30 is driven from leftto right, guide rollers 41 cause the portion of member 30 which isbetween the right end of guide 22 and connector 36 to form a loop. Thisallows for a saving in space over apparatus using a stiff carriermember. Furthermore, the use of a flexible carrier member in the mannerillustrated avoids the use of a continuous belt with its attendantdisadvantage of requiring a commutator which is subject to tonercontamination.

In operation, stylus carrier member 30 is driven from left to rightacross the recording medium 2 during the application of suitablerecording signals to the styli. During the movement of the stylus arraya predetermined amount, referred to as a character space, a character isrecorded on the electrographic recording medium 2 in the form of alatent electrostatic charge pattern. Recording medium 2 may bestationary in the recording zone during the left to right transversal 0fthe stylus array during which an entire line of characters may berecorded. At the righthand terminal point of the stylus movement, thedirection of stepping motor 10 is reversed via stepping motor controlcircuit 18. The electrostatic charge patterns recorded by thetransversal of the stylus are rendered visible by depositingelectroscopic marking particles, or toner, on these patterns. Afterdevelopment, the toner may be fixed to the recording medium in any ofseveral conventional manners. For example, recording medium support andguide member39 may have a platen fuser employing a resistance heatingcoil over which the medium is moved, thus rendering the developed imagesperma nent.

In the embodiment illustrated, engaging means 14 is selected to be asprocket wheel. The dimensions of car 'rier member 30 are selected sothat, when inserted in carrier guide 22, the perforations 34 thereon areaccessible via slot 20 to the teeth on the sprocket wheel. When thestepping motor 10 is energized for forward incrementing, the sprocketwheel rotates in the direction of the arrow and drives stylus carriermember 30 from left to right. When stepping motor 10 is energized forreverse incrementing, sprocket wheel 14 rotates in the oppositedirection, thereby driving carrier member 30 from right to left.

Various features of the drive mechanisms shown in FIG. 1, such as astylus retract mechanism have not been illustrated for the purpose ofconciseness and since such features are well known in the prior art.

Referring now to FIG. 3, there is shown a block digram of the novelstepping motor control system of the present invention. Input data, suchas data encoded into ASCIl code, comprising a-parallel seven bit patterncorresponding to a character to be printed, is applied to characterbuffer register 100. The output of character buffer register is gated tocharacter generator 102 in time sequence with the strobe, or clock,signal generated by circuitry not shown and applied to strobe controlgate 104. The output of character register 100 is also coupled tofunction decoder 106 which decodes a suitable character or a controlword to and generates a pulse to enable the stepping motor. Charactergenerator 102 converts the input code from register 100 into signalssuitable to form a representation of the character in a five by sevenmatrix format. The output of character generator 102 is connected to theinput of stylus drivers 108 which operate to amplify and shape theoutput of character generator 102. The output of the stylus drivers 108are applied to selected conductors of stylus 6 to printa charactercorresponding to the data applied to character buffer register 100. Theoutput of function decoder 106 is connected to control gate 112 whichdetermines in which direction the stepping motor is to be advanced. Theoutput of strobe control gate 104 is connected to function decoder 106and step generator 114. Character bit shift register 116 has its outputconnected to character generator 102 and to the input of step generator114. The outputs of control gate 112 and step generator 114 areconnected to the input of stepping motor control logic circuit 118 whichoperates to control stepping motor drive circuit 119. Drivecircuit 119in turncontrols stepping motor 10. The output shaft of stepping motor 10is coupled to stylus 6 to drive the stylus across the recording medium,as shown in FIG. 1, and to shaft encoder l6. Shaft encoder 16 operatesto break each step of stepping motor 10 into seven equal elements,corresponding to five columns of data and two columns of inter-characterspace, so as to provide a substantially distortion free printedcharacter. The output of shaft encoder 16 is connected to the input offeedback control gate 124 which operates to synchronize character bitshift register 116 and step generator 114. The step pulse output of stepgenerator 114 is also connected to one input of column counter anddecoder 126, the output thereof being connected to control gate 112.Initialization logic circuit 128 is connected to step generator 114 andcolumn counter 126 and operates to initialize the system when it isturned on by resetting the column counter to zero and returning stylus 6to a location corresponding to zero.

In operation, ASCII input data is applied to character buffer register100 in parallel, the output thereof being clocked into charactergenerator 102 and function decoder 106 by strobe control 104. Functiondecoder 106 steps motor when a suitable character, or a space forexample, is decoded and the signal applied to control gate 112determines whether the stepping motor is to advance or return towardsthe initial point. If the motor is to advance, a signal is applied tolead 200; if the motor is'to return, a signal is applied to lead 210.Step generator 114 applies a stepping pulse to stepping motor controllogic circuit 118, enabling the shaft of stepping motor 10 to rotate anamount dependent upon the stepping angle of the motor (for example, 5 ofrotation per step pulse). Stylus 6 moves a distance equivalent to onestep and shaft encoder 16 generates seven pulses per step. The outputpulses produced by shaft encoder 16, which are generated in both thehigh and low speed modes of operation, are fed to character bit shiftregister 116 via the feedback control gate 124. Character bit shiftregister 116 transmits to character generator 102 the second throughsixth of the seven pulses generated by shaft encoder 16 for each step ofmotor 10. These pulses strobe out each character from charactergenerator 102 in time sequence with the shaft encoder output and enablesthe five by seven data matrix to be printed by stylus 6 accurately incorrespondence with the movement of the stylus across the recordingmedium. The first bit in character bit shift register 116 on line 125,serves to step stepping motor 10. Column counter and decoder 126, resetby initialization logic 128 at appropriate times, counts the number ofstepping pulses produced by step generator 114. When the number ofpulses counted is equivalent to movement of the stylus from the initialposition tothe right-hand margin, a signal is applied to control gate112 which in turn generates a signal on lead 210 causing generator 114to reserve the direction of stepping motor 10.

Referring now to FIG. 4, the schematic logic diagram of stepping motorcontrol logic circuit 118 shown in FIG. 3 is illustrated. The outputsignal from turn around control logic 112, corresponding to drivingstylus carrier member 30 in a forward direction, appears on lead 200 andis applied to one input of NAND gates 202, 204, 206 and 208. The outputappearing on lead 210 also generated by control logic 112, is theinverse of the signal on lead 200 and is applied to one input of NANDgates 212, 214, 216 and 218. The Q output of flip-flop 220 is connectedto the other input of NAND gates 202 and 212 while the 6 output thereofis connected to the other input of NAND gates 204 and 214. The Q outputof flip-flop 222 is applied to the other input of NAND gates 206 and 216while the 6 output thereof is connected to the other inputs of NANDgates 208 and 218. The output of NAND gate 216 is coupled to the K inputof flip-flop 220 via inverter 224 while the output of NAND gate 204 isconnected to the J input of flip-flop 222 via inverter 226. The outputof NAND gates 202 and 214 are connected together and coupled to the Kinput of flip-flop 222 via inverter 228. The output of NAND gates 206and 218 are connected together and coupled to the J input of flip-flop220 via inverter 230. The CLK input of flip-flops 220 and 222 arecoupled to step pulse output 120 of step generator 114 via invertingamplifier 232.

In operation, a positive signal level appears on lead 200, correspondingto a forward step operation to be initiated. The characteristics of theTS 25-1008 stepping motor requires a predetermined time sequence ofpulses to be supplied to the stepping motor coils to get the forwardstepping operation. Assuming that the Q outputs of flip-flops 220 and222 are initially zero, the following sequence at the Q outputs willprovide forward stepping: For flip-flop 220; l,l,0,0; for flip-flop 222;O,l,l,0. The .IK flip-flops 220 and 222 each have two conditioninginputs and a clock input.

The operation and construction of .II( flip-flops is well known in theart. If both conditioning inputs are disabled at clocktime, theflip-flop will remain in its present state. If the J input is enabledand the K input is disabled, the flip-flop will be set at clocktime. Ifthe K input is enabled and the .1 input disabled, the flip-flop will bereset at clocktime. If both .I and K inputs are enabled, the flip-flopwill change states when a clock pulse occurs.

Gates 208, 206, 204 and 207 control the forward stepping inputs toflip-flops 220 and 222. Gates 218, 216, 214 and 212 control the reversestepping inputs. The outputs of the gates are wire ored as shown andinverters 226, 224, 228 and 230 correct the sense of the inputs toflip-flops 220 and 222. If in the initial state both flip-flops arereset and forward line 200 is enabled, the following count will occur:

step pulse lnit l 2 3 4 FF 220 0 O l l O FF 222 O l l O O enablingforward stepping operation. If forward line 200 is disabled and reverseline 210 is enabled, the following count will occur:

step pulse Init 1 2 3 4 FF 220 O l l 0 O FF 222 0 0 l l 0 enablingreverse stepping operation.

In summary, the logic circuitry shown in FIG. 4 provides a technique forproviding a sequence of pulses to the stepping motor coils whichdetermines whether the stepping motor is to be incremented in theforward or reverse direction.

Referring now to FIG. 5, there-is shown a schematic diagram of steppingmotor drive circuit 119 connected to stepping motor 10. Output leads300, 302, 304 and 306 (FIG. 4) are coupled as shown to the respectivegate inputs shown in FIG. 5. Input lead 300 is connected to the input ofinverter 308 and one input of NAND gate 310. Input lead 302 is connectedto the input of inverter 312 and to one input of NAND gate 314, input304 is connected to inverter 316 and to one input of NAND gate 318, andinput 306 is connected to inverter 320 and to one input of NAND gate322. The outputs of the gates set forth hereinabove are connected toinverting amplifiers 324, 326 338, respectively. The outputs of theinverting amplifiers are connected to resistors 340, 342 354,respectively, sequential pairs of resistors (340 and 342, 344 and 346,etc.) being connected to a common point and thence to the associatedstepping motor coils a, b, c and d. The other input of the NAND gates ofFIG. 5 is called the PRINT" line input. As set forth previously, thesystem described in the present invention is adapted for use in a dualmode printer system which comprises a print (or high speed) mode and acompose (or low speed) mode. It should be noted at this point that theinvention may be also utilized in a system wherein the stepping motor isdriven continuously. When the printer is conditioned to be in thecompose mode of operation, a logic is generated on the PRINT line (bymeans not shown).

The logic 0 causes a logic 1 to be present at the NAND gate outputs.However, the inverting amplifiers coupled thereto invert the logic 1into a logic 0. The current generated in resistors 342, 346, 350 and 354is of such direction as to cause the total current at the common point(and entering the stepping motor coils) to be less than if the output ofthe aforementioned inverting amplifier was a logic l. This logic 1 isgenerated when the system is in the print mode of operation, the logic 1on the print line appearing at the output of its associated invertingamplifier as a logic 0. For example, assume the system is in the composemode and the cycling sequence is at the point wherein a stepping pulsesequence has appeared on lead 302. The output of inverter 328 will be alogic 1, causing current to flow into resistor 344. Since the print lineis a logic 0, the output of inverter 330 will be at logic 0, reducingthe current tothe common point of resistors 344 and 346 and thereforereducing the current to coil b. If the system is in the print mode atthe time the pulse sequence is on lead 302, a logic 1 will appear at theoutput of inverter 330, causing current to flow through resistor 346.The total current through resistors 344 and 346 is summed at the commonpoint thereof anf flows into coil b. It can therefore be seen, assumingthat the resistors are of equal value, that the current to the steppingmotor coils in the compose mode is one-half the current to the coils inthe print mode.

Since the amount of torque and speed of the stepping motor is dependentupon the current through its coils, it can be observed that thecircuitry shown in FIG. 5 provides a simple and reliable control for thestepping motor whereby it may be utilized efficiently in both high speedand low speed modes of operation. Furthermore, additional amplifiers andresistors may be added so that a plurality of stepping speeds may beattained. in addition, further control logic may be added so thatasynchronous operation at varying speeds is achieved.

While the invention has been described with reference to its preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents substituted for elementsthereof without departing from the true spirit and scope of theinvention. in addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its essential teachings.

What is claimed is:

1. Apparatus for recording latent electrostatic images in the form ofalphanumeric characters in spaces on an insulating recording mediumcomprising a carrier member having a stylus formed thereon,

said stylus comprising a plurality of electrical conductors,

a guide member having a slot along a portion of its surface forreceiving said carrier member and holding said stylus in spatialrelation to said recording medium, said carrier member having freedom oflinear movement within said slot,

a bi-directional stepping motor coupled to said carrier member formoving said carrier member within said slot,

means responsive to input signals representing said alphanumericcharacters for energizing said stepping motor to move said carriermember between a first and a second position in discrete predeterminedsteps, and

character generating means responsive to said input signals for applyingelectrical signals to said electrical conductors to record said latentelectrostatic images on said recording medium.

2. The apparatus as defined in claim 1 wherein said discrete step ofsaid stepping motor causes said carrier member to move across saidrecording medium a single one of said spaces, said apparatus furtherincluding encoder means coupled to said stepping motor for providingsignals which represent divisions of the discrete step, said charactergenerating means being responsive to said encoder means signals forrecording characters within said spaces.

3. The apparatus as defined in claim 1 wherein said carrier membercomprises a flexible strip of material having a connector at one endthereof for connection to said character generating means, saidapparatus further including loopforming means for directing said carriermember to forma loop as said carrier member exits from said guidemember.

4. Printing apparatus comprising an insulated recording medium,

a carrier member,

a stylus comprising a columnar array of electrical conductors mounted onsaid carrier member,.

guide means for retaining said carrier member and holding said stylus afixed distance from said recording medium, said guide means includingmeans for allowing said stylus to move in a linear fashion between afirst position and a second position,

a bi-directional stepping motor coupled to said carrier member formoving said carrier member in said guide means,

control means responsive to a signal representing an alphanumericcharacter for controlling said stepping motor to move said stylus onsaid carrier member a predetermined distance from said first positiontoward said second position, and

means responsive to said alphanumeric character signal for applyingelectrical pulses to the conductors of said stylus so as to form anelectrostatic image of said alphanumeric character on said recordingmedium in the space defined by said predetermined distance.

5. The apparatus of claim 4 wherein said control means comprises meansresponsive to said stylus reaching said second position for activatingsaid stepping motor to return s aid stylus to said first position.

6. The apparatus of claim 5 wherein said carrier member comprises aflexible strip of material, said apparatus further including loopforming means for directing said carrier member to form a loop as saidcarrier member exits from said guide means when said stylus is movedfrom said first position toward said second position.

7. The apparatus of claim 5 wherein said control means comprises firstmeans controllable for generating either a first or a second set ofsignals,

second means controllable for generating either said first or saidsecond set of signals,

means for applying the signals generated by said first means and saidsecond means to said stepping motor, and

direction control means for controlling said first means to generatesaid first set of signals and said second means to generate said secondset of signals whereby said stepping motor is driven in a firstdirection and for controlling said first means to generate said secondset of signals and said second means to generate said first set ofsignals whereby said stepping motor is driven in a second direction.

8. The system of claim 7 wherein said applying means incremental motorspeed variations.

1. Apparatus for recording latent electrostatic images in the form ofalphanumeric characters in spaces on an insulating recording mediumcomprising a carrier member having a stylus formed thereon, said styluscomprising a plurality of electrical conductors, a guide member having aslot along a portion of its surface for receiving said carrier memberand holding said stylus in spatial relation to said recording medium,said carrier member having freedom of linear movement within said slot,a bi-directional stepping motor coupled to said carrier member formoving said carrier member within said slot, means responsive to inputsignals representing said alphanumeric characters for energizing saidstepping motor to move said carrier member between a first and a secondposition in discrete predetermined steps, and character generating meansresponsive to said input signals for applying electrical signals to saidelectrical conductors to record said latent electrostatic images on saidrecording medium.
 2. The apparatus as defined in claim 1 wherein saiddiscrete step of said stepping motor causes said carrier member to moveacross said recording medium a single one of said spaces, said apparatusfurther including encoder means coupled to said stepping motor forproviding signals which represent divisions of the discrete step, saidcharacter generating means being responsive to said encoder meanssignals for recording characters within said spaces.
 3. The apparatus asdefined in claim 1 wherein said carrier member comprises a flexiblestrip of material having a connector at one end thereof for connectionto said character generating means, said apparatus further includingloop forming means for directing said carrier member to form a loop assaid carrier member exits from said guide member.
 4. Printing apparatuscomprising an insulated recording medium, a carrier member, a styluscomprising a columnar array of electrical conductors mounted on saidcarrier member, guide means for retaining said carrier member andholding said stylus a fixed distance from said recording medium, saidguide means including means for allowing said stylus to move in a linearfashion between a first position and a second position, a bi-directionalstepping motor coupled to said carrier member for moving said carriermember in said guide means, control means responsive to a signalrepresenting an alphanumeric character for controlling said steppingmotor to move said stylus on said carrier member a predetermineddistance from said first position toward said second position, and meansresponsive to said alphanumeric character signal for applying electricalpulses to the conductors of said stylus so as to form an electrostaticimage of said alphanumeric character on said recording medium in thespace defined by said predetermined distance.
 5. The apparatus of claim4 wherein said control means comprises means responsive to said stylusreaching said second position for activating said stepping motor toreturn s aid stylus to said first position.
 6. The apparatus of claim 5wherein said carrier member comprises a flexible strip of material, saidapparatus further including loop forming means for directing saidcarrier member to form a loop as said carrier member exits from saidguide means when said stylus is moved from said first position towardsaid second position.
 7. The apparatus of claim 5 wherein said controlmeans comprises first means coNtrollable for generating either a firstor a second set of signals, second means controllable for generatingeither said first or said second set of signals, means for applying thesignals generated by said first means and said second means to saidstepping motor, and direction control means for controlling said firstmeans to generate said first set of signals and said second means togenerate said second set of signals whereby said stepping motor isdriven in a first direction and for controlling said first means togenerate said second set of signals and said second means to generatesaid first set of signals whereby said stepping motor is driven in asecond direction.
 8. The system of claim 7 wherein said applying meansincludes speed control means for varying the magnitude of the signalsapplied to said stepping motor whereby the speed of said stepping motormay be controlled.
 9. The system of claim 8 wherein said speed controlmeans includes a plurality of amplifiers and means for activatingselected ones of said amplifiers to provide incremental motor speedvariations.